Wireless networks are composed of devices locally generating data for remote destinations. Wireless nodes typically use wireless communication (e.g., radio transmission) to send their data to a central computer system, which accumulates the data and builds it into a larger picture. In some wireless network systems, communication among nodes is organized as a set of links, scheduled in time into a communications superframe. Each link identifies at least one node scheduled to transmit a packet during a scheduled time interval, and optionally at least one node scheduled to listen for and receive a packet during the interval. A communications scheme organized in this way saves power by minimizing the total time each node needs to have its transmitter and/or receiver powered on. The network can use several different superframes for operation, and each superframe can be designed for a different communication need (e.g., system startup, normal operation, node diagnostics, emergency purposes). Nodes can individually switch among superframes as necessary or nodes can have multiple superframes operating concurrently.
Data and control packets flow through wireless networks along paths determined based on routing graphs. The routing graphs are used to determine routes for propagating the packets from node to node through the wireless network. Wireless nodes have finite output power and hence are limited to a certain communication range. As a result, communication across the network from a source node to a remote destination node may require several retransmissions of the packet along a path through one or more intermediate nodes. Each transmission/retransmission is called a hop, and each hop passes the packet from a sender node to a receiver node. Each unordered node pair between which it is possible to exchange packets in a network is called a path. A routing graph identifies which paths are valid for a next hop of a packet's route to a destination node.
The fraction of packets transmitted by the sender that are properly received by the receiver and acknowledged on a path is called the path stability. To ensure adequate levels of performance, diagnostics are kept to quantify path stability throughout the network. The only way to certainly measure path stability is to send packets and see what fraction is acknowledged. Wireless performance on paths varies with time so it is expected that path stability changes and frequent packet sending is required to maintain an up-to-date measure of path stability.